Particle Physics

Experimentalists: Prof. Bob Clare, Prof. John Ellison, Prof. Bill Gary, Distinguished Prof. Gail Hanson, Research Physicist Ann Heinson, Assoc. Prof. Owen Long, Prof. Steve Wimpenny

Theorists: Prof. Bipin Desai, Prof. Ernest Ma, Prof. José Wudka


Experimental Program

Our experimental research takes place at three large laboratories: Fermi National Accelerator Laboratory (Fermilab), located about 45 miles west of Chicago, Illinois; the European Laboratory for Particle Physics (CERN), near Geneva, Switzerland; and the Stanford Linear Accelerator Center (SLAC) in California.

Professors Ellison, Heinson, Wimpenny, and Clare are members of the DØ Collaboration at the Tevatron proton-antiproton Collider at Fermilab. The Tevatron is the world's highest energy collider, which allows study of the heaviest elementary particles. The UCR DØ group's current research concentrates on top quark physics, including top pair production with decay into the dilepton final state (Wimpenny) and single top quark production (Heinson), and CP violation in the B_s system (Ellison). Members of the group played a major role in the discovery of the top quark at DØ in 1995, and in the design and construction of the Silicon Microstrip Tracker now being used to collect new data. At CERN, the Large Hadron Collider is planned to start running in 2008. This proton-proton machine will operate at seven times the energy of the Tevatron collider, allowing studies of much higher mass elementary particles and producing much higher statistics for precision measurements. Professors Hanson, Clare, Ellison, Gary, and Wimpenny, are members of the Compact Muon Solenoid Collaboration. The UCR researchers are active in several areas: the construction and comissioning of the silicon tracking system; the construction and commissioning of the endcap muon detection system; offline computing; and event reconstruction software. When data arrives, they expect to be leading participants in the Higgs boson physics program and searches for new physics.

Professors Gary and Long are members of the BaBar Collaboration at the Stanford Linear Accelerator Center. This experiment was the first to observe CP violation in B meson decays. Measurements from the BaBar collaboration have now established the Standard Model CKM mechanism as the dominant source of CP violation in flavor transitions, confirming a theory that stood for nearly 30 years without experimental verification. The UCR Babar group is now focused on searching for signs of new physics by studying rare B decays. Virtual particles from beyond the Standard Model can cause the CP asymmetries in penguin-dominated decays to differ substantially from the precise predictions of the Standard Model. There is a hint of such a disagreement in the current data. The UCR Babar group is responsible for the maintenance and operation of a new gas system for the instrumented flux return (muon and neutral hadron detector). The system was designed, constructed, and tested by the UCR group. Gary is also active in quantum chromodynamics research and is a member of the CTEQ Collaboration.

Professor Hanson is a member of the Neutrino Factory and Muon Collider Collaboration, which is carrying out a program of research and development towards a future muon-antimuon collider or a muon storage ring to produce an intense neutrino beam from the decays of the muons.

Theoretical Program

The field of theoretical high-energy physics has progressed enormously during the last 40 years. We have an extremely accurate theory, the Standard Model, that explains all current data. There are arguments, however, indicating that it is not the most fundamental description of nature. The UCR theory group studies modifications and extensions of the Standard Model in the hope of providing a yet more fundamental description of nature.

One of the main unknowns in the Standard Model is the origin of the masses: the data show no obvious regularity that can explain quantitatively the measured values. Desai has studied this issue through a model implementing the Nambu-Jona Lasinio mechanism. Within this formalism several properties of the mass spectrum can be understood. The gauge vector bosons as possible quark-antiquark bound states that acquire masses without invoking the Higgs mechanism, is another subject being explored by him.

Among many possible extensions of the Standard Model, supersymmetry plays a prominent role in explaining some of the parts of the theory and in providing many new and exciting predictions that can be tested Fermilab and CERN. Ma has studied several of these models as well as many aspects of neutrino physics.

Given that the Standard Model is believed to be a manifestation of a more fundamental theory, one might ask whether it is possible to probe this new theory through existing data. A consistent way of implementing this approach is based on an effective Lagrangian formalism under investigation by Wudka. He is also studying the physics of high-energy heavy ion collisions being probed at RHIC.